Answer: Because they were cheap labor.
Step-by-step explanation:
Slavery in the United States was institutionalized. A large number of Africans and African Americans were involved in slave labor. Slaves performed the hardest physical jobs and had no rights. The largest number of slaves in America worked in the south of the country on large cotton plantations, which were the main raw material in that country. Slavery in America was abolished by introducing the thirteenth amendment to the Constitution of the United States in 1865.